Styrene ≠ polystyrene: An important distinction for composites

Definitions are important when discussing technology. Although often used interchangeably, the terms styrene and polystyrene refer to different materials. Preferentially called ethenylbenzene by the International Union of Pure and Applied Chemistry (IUPAC, Zürich, Switzerland) and also known by nine other common names, styrene (C₆H₅CHCH₂ or C₈H₈) is a thick, colorless and sweet- but strong-smelling monomer derived from benzene. Polystyrene ((C₈H₈)n), on the other hand, is a solid thermoplastic polymer made up of a great many repeating units of the styrene monomer. 

Notably, styrene occurs naturally in such common plants as sweetgum-genus tree sap and foodstuff, such as cinnamon, coffee beans, peanuts, beer, beef, wheat, oats, strawberries and peaches. Further, it is found in coal tar, a byproduct of coke and gas production from coal, which, itself, is formed from fossil plants. Presently, 98% of all ethenylbenzene is extracted from natural products; only 2% is currently synthesized.

Polystyrene is an important polymer used to produce other thermoplastic copolymers, including acrylonitrile butadiene styrene (ABS), styrene acrylonitrile (SAN), acrylonitrile styrene acrylate (ASA) and, of course, foam polystyrene — the latter informally and often incorrectly called by The Dow Chemical Co. (Midland, MI, US, now DowDuPont Inc.) tradename, Styrofoam. Styrenic thermoplastics are known for their excellent surface aesthetics, good stiffness and their good adhesion to both paint and plating, making them an important class of polymers for aesthetic applications in industries that range from packaging to small appliances to automotive trim. 

On the thermoset side of the business, styrene monomer is commonly used as a reactive diluent (solvent) in vinyl ester or unsaturated polyester resins and gel coats. “The curing reaction that transforms a liquid mixture of resin, glass, fillers and other materials into a solid, durable composite product involves the crosslinking of vinyl ester and unsaturated polyester molecules by styrene,” adds John Schweitzer, senior manager with the American Composites Manufacturers Assn. (ACMA, Arlington, VA, US). “Styrene is a uniquely capable and cost-effective reactive crosslinking agent for these resins.” 

This short article is a companion Side Story to a CW feature article titled, “US styrene-reduction mandates: Go or no-go.”